Why is my plugin still not working?

Okay, you didn't actually specify which part to destroy, so:

local location = game.Workspace -- locals are faster
local children = location:GetChildren()
local itemName = "Supplies" -- name of the part you want to destroy
local supplies = script.Parent.Supplies
local x = supplies:Clone()

if #children >= 1 then -- #children is faster
    for i = 1,#children do
        if children[i].Name == itemName then
            children[i]:remove()
            x.Parent = location --  clones x for every part to destroy
        end
    end
end

Here's a fixed version of your script.

local Supplies = workspace:FindFirstChild("Supplies")
if #Supplies:GetChildren() > 0 then
    for _, child in pairs(Supplies:GetChildren()) do
        child:Destroy()
    end
end

wait(0.5)

local newSupplies = script.Parent.Supplies:Clone()
newSupplies.Parent = workspace

Here's a rundown of what changed:

I changed this part at the beginning

location=(game.Workspace) -- This is from a user here thank you guys
children=location:FindFirstChild("Supplies") -- This is from a user here thank you guys
numberofchildren=#children -- This is from a user here thank you guys
supplies = script.Parent.Supplies

to the following:

local Supplies = workspace:FindFirstChild("Supplies")

All you really needed here was the "Supplies" object in the Workspace. The rest of the variables were unnecessary. Also, a key thing to note hear is the "local" keyword before the variable name ("Supplies"). For the most part, you should use local variables in your scripts. Among other benefits, local variables can be accessed faster than global variables.

Moving on, I changed this part of your code

if numberofchildren == 1 then
    children:Destroy()
end

to this:

if #Supplies:GetChildren() > 0 then
    for _, child in pairs(Supplies:GetChildren()) do
        child:Destroy()
    end
end

Since we removed some unnecessary variables, we first do a quick check on how many children Supplies has. If it has more than 0 children, we iterate through all of the children within Supplies and destroy them. What you previously tried to do is:

children:Destroy()

The reason that does not work is because GetChildren returns an array of all of the children of an object. You can't destroy an array of an object or call any ROBLOX-related functions on an array. That's why you need to iterate through the array and destroy all of its members.

Finally, I changed this

x = supplies:Clone()
x.Parent = game.Workspace

To this:

local newSupplies = script.Parent.Supplies:Clone()
newSupplies.Parent = workspace

I directly indexed script.Parent.Supplies because we removed the variable earlier. The new method also uses a local, named variable. Like I already mentioned, most of your variables should be local. It's also a good practice for readability to name your variables appropriately, even if they're short-lived.

I hope this helped. Good luck!

Are you sure you turned the plugin on in 'Manage Plugin's'?